Plants Have an Immune System, Too
We know that animals fight disease with an army of patrols swimming in blood, but how do plants cope? They are exposed to pathogens, too: everything from bacteria to fungi, worms and insects. Without a central nervous system or circulatory system to help, are our gentle green friends at the mercy of what comes? The answer is no. In Nature Nov 16, two biologists described “the plant immune system.”1
“Plants, unlike mammals, lack mobile defender cells and a somatic adaptive immune system,” wrote Jones and Dangl, authors of the paper. “Instead, they rely on the innate immunity of each cell and on systemic signals emanating from infection sites.” These signals help special proteins distinguish self from non-self. The authors describe a two-branch and four-stage system involving numerous protein parts. Much remains to be understood, but what they wrote about is withering in its complexity. It must work pretty well, when all is said and done. In short, “Most plants resist infection by most pathogens,” they noted.
1Jonathan D. G. Jones and Jeffery L. Dangl, “Review: The plant immune system,” Nature 444, 323-329 (16 November 2006) | doi:10.1038/nature05286.
The authors use evolutionary language, but it is really superfluous. They talk about how angiosperms arose at the same time pathogens evolved to take advantage of them, and how the evolutionary arms race continues to this day. While this may satisfy the need of certain atheists to feel like they are on the path to understanding how things might make themselves, their explanations are too general for empirical verification and border on the teleological.
A fresh approach might be to view the plants and their pathogens as parts of an interacting system of checks and balances. Plants need to thrive to fulfill their roles in the ecosystem, but might overtake everything if unchecked. Pathogens are like governors on the engine or brakes at the speed limit. For their work, they get paid with plant food.
When things become unbalanced and whole populations collapse, that’s when we tend to see the pathogens as evil. Why things get unbalanced is an interesting question. Exchanging metaphors to see the scene as a Darwinian struggle for selfishness and survival, however, does nothing to help the empirical investigation of the system. It is philosophy, not science. What qualifies as science is applying principles derived from the observed cause and effect structure of the world. When we see interacting systems involving complex machines and informational systems, we infer that intelligence was involved in their origin. That’s about all science can say. Further understanding requires input from other sources.